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Discussion Starter #1
hello, finally i register this thing after almost a year working on it. i go to take it for a ride... as im pushing it out of the garage the front brake starts sticking intermittently. i figure its just the new pads wearing to the disc so i take it for a loop around the block to see if it gets any better... it starts smoking, smells of burning brakes and rotor is extremely hot. when i got the bike i rebuilt the caliper with a kit, replaced the pads, had the rotor resurfaced and changed the fluid. it worked ok for a loop around the block a week ago and was not nearly this bad, so i started bleeding the brakes. sometimes i can get it to not stick when i bleed it but if i take it more than 1/10 a mile it starts sticking again. so i rebuilt the master cylinder because at this point its the only thing i have not cleaned and it still will not go away. its not as bad as this morning when i didnt touch it but its by no means ridable. normally id just get a new caliper lines and master cylinder but this stupid bike is so damn hard (or expensive) to find parts for. please help im stumped on this one, the only possible thing i can think of is the rotor being warped slightly, but when i got it resurfaced wouldnt that fix that?
 

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Have you rebuilt the master cylinder?? or at least pull it apart and clean out the internal valve.


brake lines I order by length and fittings needed on each end from aftermarket suppliers..
rather partial to stainless braided lines..

Did you lubricate the Caliper Pins? Lithium White grease is what I use. the caliper needs to slide freely on the pins..

Yes, surfacing the disk should eliminate warpage if done properly..
 

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If you remove the rotor and lay it on a sheet of glass, any warpage should be evident. Did you measure the thickness of the rotor after turning to see if it's still in spec? Like you, I'm wondering if the brake line is the problem. When you rebuilt the calipers, did you clean the pins the pads move on and put a light coating of silicone base grease on them?
 

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Discussion Starter #4
If you remove the rotor and lay it on a sheet of glass, any warpage should be evident. Did you measure the thickness of the rotor after turning to see if it's still in spec? Like you, I'm wondering if the brake line is the problem. When you rebuilt the calipers, did you clean the pins the pads move on and put a light coating of silicone base grease on them?
the rotor is 4.5mm after the turning (spec is 4mm). i took it to a machine shop when my dad needed some other stuff machined, the guy seemed like he knew what he was doing and it came out looking near new. i completely disassembled and cleaned the master cylinder today after trying bleeding the brakes multiple times (as it was the only thing i had not cleaned up to this point). i cleaned all the braking parts on a wire brush wheel (motor with wheel attachment) including the pistons which had some corrosion (very light pitting on them after cleaning). i greased the caliper pins with brake grease and put the boots on. everything done according to the manual. i even just tried loosening the caliper bolts and squeezing the lever to align the caliper then tightening everything up (had this problem on my 250 before and that fixed it) but the problem persists.
 

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Sounds like you have covered all the bases so far. Maybe the brake line is deteriorated internally, blocking the flow of the fluid?
 

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Discussion Starter #6
Sounds like you have covered all the bases so far. Maybe the brake line is deteriorated internally, blocking the flow of the fluid?
what im thinking at this point... it says 1/8" sae on the line; i cant find any new direct replacements. the part number for it is 45126-MM2-671. so how would i go about replacing the line? the connectors look ok but they look crimped onto the line somehow and i dont know i could get them off without damaging them, let alone get them onto a new line. how should i go about this? thank for the speedy responses!
 

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Discussion Starter #8
These guys can build a brake line to your specs. https://www.ebay.com/usr/rennsportautoparts?_trksid=p2047675.l2559

Describe the length and angle of the end fittings and they can make it up in braided stainless steel.
https://www.ebay.com/itm/115cm-45-M10-Brake-Oil-Hose-Line-Banjo-Fitting-Stainless-Steel-End-PM/401794459673?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
i ended up ordering this. i got a measuring tape for tailoring and ran it along the brake line, taping it in multiple sections. it was about 43" but i ordered a 45" line to account for any human error, better slightly longer than shorter right? i also measured the inside of the eyelet for the bango bolt with my precision caliper and it was just about 10mm (i couldnt get it to fit into the widest point but it was reading like 9.9-9.95mm so ill assume thats a 10mm). so i ordered this "universal" stainless brake line with m10 banjo fittings. lets hope this ebay special "universal" part is actually what it claims to be. ill update when its here.
 

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What you have to be concerned about is how much angle/bend there is on the fittings, and if the ends are in the same plane or offset. That line may be long enough to accomodate any "twist" in the line
 

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Discussion Starter #10
What you have to be concerned about is how much angle/bend there is on the fittings, and if the ends are in the same plane or offset. That line may be long enough to accomodate any "twist" in the line
the angle on the fittings looks about the same as the one currently on the bike. thats a good point about the ends being plane or offset, why i ordered a little extra. thanks for the help! ill update when its here if its fixed.
 

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I had a similar issue when I fully rebuilt my brake system and had actually replaced the front rotor. I checked the crap out of everything, but then replaced the pad spring with another I had and it seemed to solve.

I built my own SS brake cable with bango ends and line from Revival Cycles

https://shop.revivalcycles.com/motorcycle-parts/brake/

Buy an extra inch or two b/c you might have to (re)work it: it must be done properly to handle the pressure or it will pop off when squeezed.

Worked out pretty well, improved response a lot and I love the look.
 

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Discussion Starter #12
I had a similar issue when I fully rebuilt my brake system and had actually replaced the front rotor. I checked the crap out of everything, but then replaced the pad spring with another I had and it seemed to solve.

I built my own SS brake cable with bango ends and line from Revival Cycles

https://shop.revivalcycles.com/motorcycle-parts/brake/

Buy an extra inch or two b/c you might have to (re)work it: it must be done properly to handle the pressure or it will pop off when squeezed.

Worked out pretty well, improved response a lot and I love the look.
so i replaced the line today... nothing, still sticking :frown2: on the bright side the line seems to work fine so at least that has been eliminated. i ordered a pad spring the same day as the line so that should be here soon. i really hope that guy didnt screw up my rotor resurfacing it
 

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so i replaced the line today... nothing, still sticking :frown2: on the bright side the line seems to work fine so at least that has been eliminated. i ordered a pad spring the same day as the line so that should be here soon. i really hope that guy didnt screw up my rotor resurfacing it
Ug.

You could likely find a nice used rotor on ebay and put it on maybe w/new pads?

When you rebuilt the rotor, did you replace the rubber piston rings? Did you lube them w/ brake fluid and feel the pistons slide in and out smoothly before you put it back together? You may have one that is not 'retracting' (if you will) maybe b/c its remaining under pressure for some reason after you release the lever? You can check by popping off the caliper and squeezing the lever. I would watch the pistons closely for unified movement and not pull the lever all the way as you will need to push them in to slide back over the caliper after. I have had success by using a thick hardwood shim and leverage-like pressure while releasing the bleed screw a bit at the same time. You should feel them go back smoothly.

I think your issue ids in the caliper. Wondering it the MC (internals) could be malfunctioning/worn and keeping the pressure high? Did you rebuild the MC?


Hope you can figure it out:)
 

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This same symptom happened on my 1985 250 Rebel. Turns out in my case the tiny pin sized hole in bottom of master cylinder was slightly clogged. That prevented all the fluid from returning out of caliper when brake lever was released. Like the OP i checked everything. Did not notice it was plugged with old fluid gum.
 

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Discussion Starter #15 (Edited)
Ug.

You could likely find a nice used rotor on ebay and put it on maybe w/new pads?

When you rebuilt the rotor, did you replace the rubber piston rings? Did you lube them w/ brake fluid and feel the pistons slide in and out smoothly before you put it back together? You may have one that is not 'retracting' (if you will) maybe b/c its remaining under pressure for some reason after you release the lever? You can check by popping off the caliper and squeezing the lever. I would watch the pistons closely for unified movement and not pull the lever all the way as you will need to push them in to slide back over the caliper after. I have had success by using a thick hardwood shim and leverage-like pressure while releasing the bleed screw a bit at the same time. You should feel them go back smoothly.

I think your issue ids in the caliper. Wondering it the MC (internals) could be malfunctioning/worn and keeping the pressure high? Did you rebuild the MC?


Hope you can figure it out:)
This same symptom happened on my 1985 250 Rebel. Turns out in my case the tiny pin sized hole in bottom of master cylinder was slightly clogged. That prevented all the fluid from returning out of caliper when brake lever was released. Like the OP i checked everything. Did not notice it was plugged with old fluid gum.
I cleaned the master cylinder already, parts looked ok and nothing was plugged up. I needed to go to a machine shop for some parts for my dad so I took the rotor and as soon as he saw it he said it was the cause. I asked him to mic it and he did and there were .2mm variances in spots on the rotor which could defiantly cause what I'm experiencing. I found a rotor off a bike with 2500 miles that looks decent for a decent price considering a new one is almost $300 from germany. I also found a cheap set of new oem pistons because mine were a little pitted after cleaning up. The seals were new when I tested this, its possible the pitting was causing some resistance with retraction. I also replaced the pad spring because DNC said it could be another potential cause. The parts will be here tomorrow, we'll see if this solves it.
 

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Some piston retraction is accomplished by deforming the square cut seal..
bottom of caliper seal groove is typically machined at a slight angle aiding the seal to twist slightly while piston is pushed out by the brake fluid. The deformed seal helps pull the piston back when the pressure is released, allowing pads to move away from the rotor more easily.

piston pitting is caused by water corroding them... Brake fluid is hydrophobic (attracts water out of air)..
Water being heaver than oil (brake fluid) collects over decades at lowest point..
bleeder is at top of caliper, No one ever removes caliper to turn upside down when they flush with new fluid..
that water just sits at the bottom of caliper corroding away till someone pops out the caliper pistons...
 

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Still a good idea to double-check that almost microscopic tiny hole in bottom of the master cylinder. I missed it when i completely rebuilt and cleaned the master cylinder and caliper and brake line. That tiny port is almost invisible. Brake cleaner did not get it cleared out, i ended up using tiny needle and wire strand and compressed air. If it is not fully clear the caliper pistons will remain in brake on position even when the brake lever is released. It visually looked open to me when examined but found internally it was not. Bought the Rebel new back in 1985 and that brake stuck problem is the first time the cycle completely stumped me for a period of several days. lol
 

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Discussion Starter #18 (Edited by Moderator)
Some piston retraction is accomplished by deforming the square cut seal..
bottom of caliper seal groove is typically machined at a slight angle aiding the seal to twist slightly while piston is pushed out by the brake fluid. The deformed seal helps pull the piston back when the pressure is released, allowing pads to move away from the rotor more easily.

piston pitting is caused by water corroding them... Brake fluid is hydrophobic (attracts water out of air)..
Water being heaver than oil (brake fluid) collects over decades at lowest point..
bleeder is at top of caliper, No one ever removes caliper to turn upside down when they flush with new fluid..
that water just sits at the bottom of caliper corroding away till someone pops out the caliper pistons...
So I replaced the rotor, pistons, and pad spring and now we're sticking all over. Mind you at this point I've also rebuilt the caliper with a kit, cleaned and inspected the master cylinder (yes I cleaned both holes completely) and replaced the brake line. at first it seemed ok, the pads were only lightly grazing the rotor, no audible noise, no noticeable drag when pushing the bike. So I decided (after taking it for a shorter test ride the night prior) to take it to the local deli about 3 miles away. The ride up seemed ok, the brake lever did progressively get harder though. When i got there I went in, grabbed a drink, came out to leave and the bike started sticking, I could feel it depressing the forks. I went over a speed hump, and BOOM the forks slam down, the front brake had completely locked. (it even left a skid on the yellow speed hump :surprise:) Mind you this is in the middle of a parking lot exit, lucky there was no one behind me. I managed the move the bike out of the way by just powering through with the engine until i was to safety, and cracked the bleeder with the provided tool kit (thank God this bike has one) and rode home without touching the front brake. That downhill ride home was the ride of my life (literally). So I got home, ordered a master cylinder rebuild kit; because at this point its the only part I haven't rebuilt. I can't ride my 250 because I was waiting for parts, so I decided to take its known working master cylinder plunger and give it a try. The lever feel improved a little, but it would seem that when the braking system gets hot, the parts are expanding or something and lessening the tolerances causing more brake drag than when the system is cool. I found this video,
where a guy bench tests a caliper. He puts a used pad in the pad spring, uses compressed air to shoot the pistons to the pad, and shows the pistons visibly retracting into the caliper. He said, like SoakedKarma the square seals are deforming when fluid is pushed through and causing the retraction when pressure is released. He also stated that corrosion under the seals can cause extra pressure to the pistons, causing them to not retract correctly. So I removed my seals, got the 0000 steel wool and polished those suckers till they shined. But i cant for the life of me get my pistons to retract any visible amount, let alone as much as shown in the video. But I replaced the seals and pistons??? The pistons isn't too difficult to depress into the caliper, I can do it with my thumbs but it doesn't want to move back out in on its own. What could be causing this at this point as I have replaced all the parts to wear? This is the most finicky brake I've ever dealt with :nonono:
 

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Discussion Starter #19 (Edited)
So I replaced the rotor, pistons, and pad spring and now we're sticking all over. Mind you at this point I've also rebuilt the caliper with a kit, cleaned and inspected the master cylinder (yes I cleaned both holes completely) and replaced the brake line. at first it seemed ok, the pads were only lightly grazing the rotor, no audible noise, no noticeable drag when pushing the bike. So I decided (after taking it for a shorter test ride the night prior) to take it to the local deli about 3 miles away. The ride up seemed ok, the brake lever did progressively get harder though. When i got there I went in, grabbed a drink, came out to leave and the bike started sticking, I could feel it depressing the forks. I went over a speed hump, and BOOM the forks slam down, the front brake had completely locked. (it even left a skid on the yellow speed hump :surprise:) Mind you this is in the middle of a parking lot exit, lucky there was no one behind me. I managed the move the bike out of the way by just powering through with the engine until i was to safety, and cracked the bleeder with the provided tool kit (thank God this bike has one) and rode home without touching the front brake. That downhill ride home was the ride of my life (literally). So I got home, ordered a master cylinder rebuild kit; because at this point its the only part I haven't rebuilt. I can't ride my 250 because I was waiting for parts, so I decided to take its known working master cylinder plunger and give it a try. The lever feel improved a little, but it would seem that when the braking system gets hot, the parts are expanding or something and lessening the tolerances causing more brake drag than when the system is cool. I found this video, https://www.youtube.com/watch?v=IVHdhXXNReQ where a guy bench tests a caliper. He puts a used pad in the pad spring, uses compressed air to shoot the pistons to the pad, and shows the pistons visibly retracting into the caliper. He said, like SoakedKarma the square seals are deforming when fluid is pushed through and causing the retraction when pressure is released. He also stated that corrosion under the seals can cause extra pressure to the pistons, causing them to not retract correctly. So I removed my seals, got the 0000 steel wool and polished those suckers till they shined. But i cant for the life of me get my pistons to retract any visible amount, let alone as much as shown in the video. But I replaced the seals and pistons??? The pistons isn't too difficult to depress into the caliper, I can do it with my thumbs but it doesn't want to move back out in on its own. What could be causing this at this point as I have replaced all the parts to wear? This is the most finicky brake I've ever dealt with :nonono:
So the master cylinder kit came today, I installed it and... nothing. I somewhat expected this because i already tried the one from my 250 but I was really hoping this would do, something. The lever is ever so slightly softer now but at this point I dont feel safe riding the bike. when the wheel is in the air i cant get more than half a rotation out of it spinning it as hard as i can. Ive already cleaned under the caliper seals as best as i can and replaced them, cleaned the passages in master cylinder, replaced the pistons, replaced the pads and spring, replaced the line, and replaced the rotor. Anyone got any suggestions? at this point im at a loss.
 

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The only other thing I can think of is a Blocked Pressure Relief/Compensating/Vent Port
can you see the piston rubber seal retract past the relief port as you release the brake handle?..

Does a small squirt of brake fluid come out of that port as brake applied?..
Wondering if Master Cylinder piston isn't fully retracting
 
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